Various proposals have been made for backwards-compatible enhancements to the vestigial sideband (VSB) modulation digital video broadcast standards promulgated by the Advanced Television Standards Committee (ATSC). One such proposal allows transmission of robustly coded information multiplexed with standard VSB information. FIG. 4 is a simplified high-level block diagram of the proposed system. The transmission system 400 includes data inputs 401a and 401b receiving the normal and robust data, respectively. The received normal and robust data are switched by multiplexer 402 under the control of control unit 403 based on a field sync signal, then randomized by a conventional VSB data randomizer 404. The randomized data stream is then Reed-Solomon coded by coder 405, and the coded data is processed into packets and interleaved by packet formatter 406 and interleaver 407, after which the interleaved data is trellis coded by encoder 408, also controlled by control unit 403.
A parity byte generator 409 operates in conjunction with trellis encoder 408 to generate parity data for interleaver 407. The encoded data from trellis encoder 408 is switched by multiplexer 410 with field sync and segment sync signals received on synchronization inputs 411a and 411b, respectively. The resulting data is combined with a pilot signal, modulated and up-converted by signal transmission module 412 and transmitted from antenna 413 over the satellite or terrestrial transmission channel.
System 400 requires adaptation of the encoder at the transmitter side. If the enhancements proposed could be implemented on the studio side, the encoder at the transmitter side could remain an existing VSB encoder, with only minor changes. There is, therefore, a need in the art for enhancing VSB transmission systems to allow multiplexing of standard and robust data while utilizing an existing encoder on the transmitter side.